As shown in FIG. 17, a conventional PTC heating device of this kind typically comprises a PTC thermistor element 1 in the form of a ceramic plate, a pair of opposite electrodes 3 formed on its opposite major surfaces to the thickness of approximately 10 micrometers by flame spraying, ion plating or printing, a pair of corrugated fin plates 5 placed on external major surfaces of the opposing electrodes 3, and a pair of fin covers 7 placed over the external sides of the corrugated fin plates 5. The corrugated fin plates 5 are securely attached to the opposing electrodes 3 by a bonding agent, and an electric contact is established between the corrugated fin plates 5 and the opposing electrodes 3.
Also known, is the structure in which a PTC thermistor element 1 having opposing electrodes 3 is clamped between a pair of metallic radiation fin plates 9 which are pressed toward each other by fastening screws 11 and nuts 13 as shown in FIG. 18.
When using these PTC thermistor heating devices, an AC voltage is applied across the opposing heat radiation fin plates 5 or 9 to heat up the PTC thermistor element 1.
However, since bonding agents generally have lower heat conduction effciencies than metallic materials, simply pressing heat radiation fin plates 9 against the opposing electrodes 3 either directly or via a bonding agent may not be sufficient to ensure a satisfactory heat conduction therebetween. Therefore, it has been desired to improve the efficiency of heat conduction between electrodes and heat radiation fin plates to the end of improving the thermal output of the PTC thermistor heating device.
Under this circumstance, the inventors focused their attention to the process of brazing two metallic parts, and completed the invention by overcoming problems related with brazing.